The present invention relates generally to brake systems for motor vehicles, and relates more specifically to a master cylinder having a proportioning valve and providing a by-pass function.
The master cylinders on many motor vehicles operate through two separate and independent pressure circuits. In a front-to-rear split system, both front brakes are connected to one chamber of the dual master cylinder and both rear drums are connected to the other chamber. Front-to-rear split systems known as xe2x80x9cHxe2x80x9d split systems normally have a proportioner installed in the brake lines between the master cylinder and the rear brakes to improve front-to-rear balance at high deceleration. At a given pressure in the circuit, often referred to as the xe2x80x9cknee point,xe2x80x9d the proportioner valve causes the rear brake pressure to rise at a slower rate than the master cylinder pressure. Conventional designs locate the proportioner valve in a separate enlarged boss on the master cylinder casting, in a screw-in module, or remotely elsewhere in the vehicle.
The present invention is a master cylinder comprising a primary piston, a secondary piston, and a proportioner valve. The secondary piston is engaged with the primary piston, and the proportioner valve is disposed within the secondary piston.
Accordingly, it is an object of the present invention to provide a master cylinder of the type described above that includes a proportioner valve.
Another object of the present invention is to provide a master cylinder of the type described above that provides a by-pass function to provide sufficient pressure to a rear brake circuit in limited circumstances.
Still another object of the present invention is to provide a master cylinder of the type described above that fits within the general packaging of the master cylinder bore.
These and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.